As a method for producing resin particles is known a seed polymerization method. The seed polymerization method is a method for absorbing a monomer contained in an aqueous emulsion in spherical seed particles of a polymer previously produced in an aqueous solvent and then polymerizing the monomer. In this method, resin particles with high sphericity reflecting the sphericity of the seed particles can be formed.
Resin particles are easy to control their characteristics by adjusting polymerization components, a crosslinking density, etc. Therefore, resin particles are used as additives for coating agents to be used for painting materials, paper, information recording paper, light diffusion films, etc., and additives for cosmetics.
However, in recent years, since characteristics which cannot be obtained in the case of high sphericity are obtained, resin particles controlled to have deformed shapes as particle shapes are produced and used as the above-mentioned additives.
For example, Japanese Patent Application Publication No. 2000-38455 (Patent Document 1) discloses a method for producing approximately flat resin particles by a seed polymerization method.